The present invention pertains to a parallel folded filter with a folded filter blank and to a process for preparing a parallel folded filter.
In a parallel folded filter known from the state of the art, a folded filter web is led on both sides to tubular nozzles, by which a self-curing plastic is pressed into the filter web. A plastic ring, which traverses the filter web, is formed upon curing the plastic, as a result of which a tight closure is formed between the plastic ring and the filter web. The filter material located outside the plastic ring is subsequently cut off, so that a round folded filter insert is left, which can be inserted into a corresponding filter housing.
A relatively large amount of plastic is needed in the prior-art parallel folded filter to completely fill out the edge area between the folds. In addition, the removal of the filter insert from the tubular nozzles is made difficult by adhesion effects of the plastic on the inner walls of the tubular nozzles. A parallel folded filter of this type has been known from DE-PS 12 75 870.
In other prior-art parallel folded filters, the folded filter web is first inserted into a filter housing and liquid sealant is then fed in while rotating the filter housing. The sealant is distributed on the inner wall of the filter housing due to the centrifugal force and seals the filter web against the housing. Such a filter is expensive to manufacture and a relatively large amount of sealant is needed, because the entire inner surface of the filter housing must be wetted with sealant.
The basic object of the present invention is to improve a parallel folded filter such that good sealing is achieved between the folded filter web and the filter housing with the smallest possible amount of sealant.
According to the invention, a parallel folded filter is provided with a prefolded blank providing a flat elliptical filter blank with fold lines. The rows of fold lines of the filter blank extend at right angles to an axis extending in the direction of the greatest longitudinal extension of the filter blank. A circumferential contour of the filter blank is dimensioned such that the filter blank assumes a circular shape with the fold formed along the fold lines (a stood up fold position). An adhesive bead extends along a circumferential contour. A ring-shaped filter housing is provided with an inner contour designed to accommodate the folded filter blank. The filter housing has a circumferential support surface for the adhesive bead.
According to another aspect of the invention, a process is provided for preparing a parallel folded filter. A filter blank with fold lines (prefolded) is prepared, in which the rows of fold lines are directed at right angles to an axis extending in the direction of the greatest longitudinal extension of the filter blank. The circumferential contour of the filter blank is dimensioned such that it assumes a circular shape with the folds stood up. An adhesive bead is applied along the circumferential contour. With the folds stood up (i.e., with the fold formed along the fold lines), the filter blank is placed into a ring-shaped filter housing, whose inner contour is designed as a support surface for the adhesive bead.
The advantage of the present invention is essentially that the sealant is applied only in the areas of the filter blank where it is needed for sealing against the filter housing. To prepare the filter blank, an elliptically extending adhesive bead is first sprayed onto a flat filter web, with fold lines based on a prefold. The filter web is then stood up (i.e., with the fold formed along the fold lines) and the filter blank is cut out of the filter web along the outer edge of the adhesive bead.
The circumferential contour of the adhesive bead is dimensioned such that with the folds stood up, a circular shape is obtained for the filter blank. In addition, the adhesive bead is positioned on the filter web such that the rows of folds extend at right angles to the axis of the greatest longitudinal extension of the filter blank. A plurality of filter blanks may be arranged next to one another or one behind the other on a filter web, so that the filter web can be utilized without appreciable waste. The filter blank is then inserted into a filter housing, and the adhesive bead extends in a zigzag pattern over the area of the inner surface of the filter housing.
In addition to the adhesive bead, the filter blank is advantageously also provided with individual bead-like adhesive tracks, which extend in parallel to the axis of the greatest longitudinal extension and act as spacers for the folds.
The process according to the present invention for preparing a parallel folded filter is characterized by the following steps:
a flat, filter blank is prepared with fold lines (preferably based on a previous fold or prefold), in which the rows of fold lines extend at right angles to an axis extending in the direction of the greatest longitudinal extension of the filter blank,
the circumferential contour of the filter blank is dimensioned such that it assumes a circular shape with the folds stood up,
an adhesive bead is applied along the circumferential contour and the filter blank with the folds stood up is placed into a ring-shaped filter housing.
A further advantageous step of the process may be provided including heating the filter housing with the folded filter blank inserted to the melting point of the adhesive, as a result of which the adhesive bead becomes attached to the inner surface of the filter housing. Complete sealing of the edge of the filter blank against the filter housing is achieved as a result. The connection between the adhesive and the inner surface of the housing is supported by rotating the filter housing during the heating.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference is made to the accompanying drawings and descriptive matter in which a preferred embodiment of the invention is illustrated.